Lancets are used in diagnostic applications to withdraw a small amount of blood by pricking a part of the body (usually the finger or the ear-lobe). In the past, the puncturing procedure had been carried out by trained, specially educated personnel either manually or using a simple apparatus. This method to obtain a blood sample is acceptable when blood investigations must only be carried out occasionally, since in this case the pain associated with the puncturing does not play a decisive role.
The requirements for blood withdrawal are substantially more stringent when regular monitoring of certain analytic values in the blood of a patient is necessary. This is particularly the case for diabetics whose blood sugar levels must be monitored frequently and regularly in order to keep these levels (which depend on food ingestion, physical activity and other factors) within certain limiting values through the administration of insulin injections. Such an intensive blood sugar therapy is of extreme importance to the health of the patient and requires at least four blood withdrawals per day. For example, the publication “The Effect of Intensive Treatment of Diabetes on the Development and Progressing of Long-term Complications in Insulin-dependent Diabetes Mellitus,” of the Diabetes Control and Complications Trial Research Group, New England Journal of Medicine, 1993, 977 to 986 reports that intensive therapy, involving at least four blood samples per day, can reduce the probability of retinopathy (which eventually leads to blinding of the patient) by 76%. This is also the case for other serious long term damage associated with diabetes mellitus.
Long-term intensive blood sugar therapy is only feasible by so-called “home-monitoring,” carried out by the patient himself or by family members without the use of trained medical personnel. The willingness and ability of the patient to obtain a blood sample by means of a lancet at least four times daily depends decisively on the properties of the blood withdrawal device. It is desirable that the pain associated with generation of the wound necessary for blood withdrawal is as low as possible. It is also desirable that the device be as simple to operate as possible, since a large share of the patients are, due to their illness or advanced age, not capable of carrying out difficult manual operations in a precise fashion. In addition, low weight and a practical shape are desirable in order that the device can be easily carried along with the patient. Also, the design should be as simple as possible, durable, and inexpensive.
Blood withdrawal devices and associated lancets have been proposed having various structural configurations to satisfy these design parameters. They are described, by way of example, in the following U.S. Pat. Nos. 4,442,836; 4,535,769; 4,469,110; 4,653,513; 4,895,147; 4,924,879; 5,318,584; 5,554,166. Although these known designs provide substantial improvements in blood withdrawal for diagnostic purposes, they are inadequate for various reasons. In particular, those devices which produce the wound with very low pain levels have disadvantages with regard to handling and/or shape and size of the device. Conversely, small and easily operated devices are typically associated with insufficiently low pain levels.
The present invention provides a device for withdrawing blood for diagnostic applications, comprising an elongated housing on the front end of which an exit opening is provided for the tip of a lancet, a lancet which can be displaced within the housing in the direction of its main axis along a predetermined puncture path, a lancet guide for guiding the lancet along the predetermined puncture path and a lancet drive having a resilient drive spring which can be locked in a loaded state using a locking device and which converts the relaxing motion of the drive spring into a puncture motion after the locking device is released, wherein the lancet is moved with high velocity along the predetermined puncture path in the puncture direction until its tip exits out of the exit opening to produce a wound in a part of the body proximate the exit opening, and wherein a two-sided rotary/translatory transmission is provided in the housing for converting the motion of a loading element movable along a linear loading path into a rotational motion of a lancet drive rotor which rotates about a rotational axis running parallel to the axis of the device to load the lancet drive rotor by tensioning the drive spring, and for converting, after release of the lancet drive, a rotational motion of the lancet drive rotor driven by the drive spring into the puncturing motion in the direction of the main axis.
The present invention also provides a blood withdrawal kit comprising the following mutually adapted system components: a blood withdrawal device in accordance with the invention and lancets adapted to be held in and used with the device. Such blood withdrawal kits (which also can be referred to as blood withdrawal equipment) are initially sold in the form of a packaged unit containing both system components. Since the lancets can normally be used only once, they are also provided in separate packages for use by patients already having blood withdrawal devices.
The term “transmission” is to be understood in its general sense (i.e., in terms of a kinematic device for coupling and converting motion). In the present case, the double sided rotary/translatory transmission transforms a translation motion of the loading element into a rotational motion of the lancet drive rotor and a rotational motion of the lancet drive rotor into a translational motion of the lancet.
Embodiments of the invention should take into consideration the fact that a low-pain puncture requires a very rapid and precise puncturing motion. To this end, it is desirable that the drive spring have a high spring constant. On the other hand, the loading element should be sufficiently easy to operate such that older and physically handicapped people can load the blood withdrawal device.
In accordance with one embodiment of the invention, the lancet drive rotor comprises a surface running along a helical path and the loading element comprises a loading cam having a contact surface that moves on the surface of the helical path to convert a linear motion of the loading element into a rotational motion of the lancet drive rotor. The helical path may be formed on a loading sleeve that operates in cooperation with the drive rotor. The forward end of the loading sleeve facing the exit opening may be designed to surround a lancet holder holding the lancet.
In accordance with another embodiment of simple construction and having low vibration, a guiding cam is provided in proximity to the front end of the transmission. It controls, in cooperation with a guide pin provided on the lancet holder, the puncturing motion and the return motion of the lancet holder and the lancet contained therein. Control of the puncturing and return motions through cooperation between a guide pin and a guide cam is disclosed in the above-mentioned U.S. Pat. Nos. 5,318,584 and 5,554,106.
These and other features of the present invention described above, will be readily apparent to those skilled in the art upon reference to the following description and the accompanying drawings.